The present invention generally relates to global landing systems (GLSs) and more particularly relates to fitting aircraft with GLSs, and even more particularly relates to methods and apparatus of fitting GLSs on aircraft also having instrument landing systems (ILSs) and/or autopilots (A/Ps).
In the past, ILSs have been used in a wide variety of airports, including military and commercial, as well as general aviation airports. These ILSs are well known in the art. However, with the advent of satellite navigation, avionics engineers are endeavoring to expand the availability of electronically aided landing systems to smaller airports, especially those previously unsupported with ILS, and to enhance the precision of approaches at airports already equipped with ILS. Many new aircraft are being delivered today with integrated multi-mode receivers on-board. These multi-mode receivers include receivers for receiving terrestrially transmitted ILS signals, as well as satellite transmitted GPS signals. They are typically integrated with the A/Ps or flight control computers (FCCs) on these new aircraft. Typically, the A/Ps and the ILS receivers require careful integration to assure proper use of glideslope and localizer deviation signals provided by the ILS receiver. Each model of aircraft is required to be separately certified by aviation regulators because of the peculiarities associated with each aircraft type and each receiver/antenna installation. Consequently, the cost of retrofitting new GLSs to existing aircraft can be expensive, especially if changes are required to be made in the A/P software which require recertification. Others have proposed various schemes for integrating GPS receivers with ILS receivers, for the purpose of reducing the recertification requirements.
While these GPS/IILS integration and retrofitting techniques may have many advantages in particular uses, they also have significant drawbacks. One common drawback of these designs is that they have not fully addressed the requirements for high precision in determining and processing glideslope and localizer deviation signals, especially during the final stages of approach and landing. At these stages, the requirements for precision become acute, and errors of position determination on the order of the length of the aircraft itself can be critical.
Consequently, there exists a need for improved methods and apparatuses for retrofitting GLSs into aircraft previously fitted with ILSs and A/Ps or FCCs.
It is an object of the present invention to provide an aircraft with a high precision global landing system.
It is a feature of the present invention to utilize predetermined guidance control points on the aircraft.
It is an advantage of the present invention to enable the precise computation of glideslope and localizer deviation signals within the GLS system.
It is another object of the present invention to provide a cost-effective method for determining and calibrating these guidance control points and the systems using them.
It is another feature to utilize a method of simultaneously measuring, with GPS receivers, the displacement of ILS receiver antennas from installed GPS antenna locations on the aircraft.
It is another advantage of the present invention to provide a quick and cost-effective method for establishing the guidance control points and the necessary corrections resulting from the frequent separation of GPS antennas, which are often midship and on the top of the aircraft, from ILS antenna locations, which are often in the nose or tail sections.
The present invention is an apparatus and method for retrofitting GLSs on aircraft previously fitted with ILSs and A/Ps or FCCs, which is designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features and achieve the already articulated advantages. The present invention is carried out in an xe2x80x9cantenna separation error-lessxe2x80x9d manner in a sense that the errors introduced by the physical separation of GPS antennas from glideslope and localizer antennas have been greatly reduced.
Accordingly, the present invention is a GLS which uses guidance control points and the separation of these points from installed GPS antennas, to generate and utilize precise glideslope and localizer deviation signals.